Re: [HACKERS] float output precision questions

[Pedro Miguel Frazao Fernandes Ferreira]

Peter Eisentraut wrote:

Matlab has a toolbox fucntion, claiming maximum precision, to convert
from its double type (PostgreSQL float8) to string which does a
sprintf('%25.18g',number).

Do we have some mathematical guarantee that this is sufficient and
necessary?  If so, then it might do.

It is necessary if you want to do this type of (huge amount of number storage) application:

[Some client] (insert) [PostgreSQL] (query) [Some client]
(double number a)-------->(float8 number)------->(double number b)

In order for a=b this is necessary. With current float8 output this is not allways true.

Here is the help for that particular Matlab function:

NUM2MSTR Convert number to string in maximum precision.
S = NUM2MSTR(N) converts real numbers of input
matrix N to string output vector S, in
maximum precision.

See also NUM2STR.

If you want I can try to contact the guys who coded this function to know
if this is sufficient.

Thanks,
Pedro M. Ferreira
--
----------------------------------------------------------------------
Pedro Miguel Frazao Fernandes Ferreira
Universidade do Algarve
Faculdade de Ciencias e Tecnologia
Campus de Gambelas
8000-117 Faro
Portugal
Tel./Fax: (+351) 289 800950 / 289 819403
http://w3.ualg.pt/~pfrazao


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